The ancestor of eukaryotes, an already complex organism
The term “simple” is often associated with “ancient” in the field of evolution. Indeed, the more simple an organism, the more we tend to consider it ancient (and vice versa). This excessively limited vision of things has once again been put to the test by researchers in Liège. The latter have discovered that the machinery of the last common eukaryotic ancestor was already highly complex, especially in terms of the RNA maturation process.
Several proteins for a single gene
Up until recently, it was commonly agreed that a gene encodes a specific protein through the intermediary of a mature mRNA that is generated after the constitutive splicing of a pre-mRNA. Constitutive splicing means that every intron is eliminated and every exon is retained in the final mRNA. This traditional set-up was completely turned upside down several years ago by the discovery of another type of splicing: alternative splicing. Contrary to constitutive splicing, this second form of splicing doesn't strictly result in the exclusion of all the introns and the inclusion of all the exons in the mature mRNA. Depending on various as yet unknown events, during alternative splicing, some exons may not be retained and some introns may be included in the mature mRNA. Hence, the expression of a gene may lead to the formation of several different mRNA and therefore the production of several different proteins, or protein isoforms.